Compact discs have been a unique article of commerce for the last few years. This new information storage device utilizes a laser beam for reading the information stored therein by the reflection of the laser off a metallic layer through a material which has molded in data bits in the form of pits and lands. The data bit pattern alters the intensity of the reflected laser to produce digital information. Materials used in the compact discs have been various plastics such as polymethylmethacrylate and polycarbonate. Polycarbonates employed in this application are described in U.S. Pat. No. 4,514,357 wherein a very low molecular weight bisphenol-A polycarbonate, the average molecular weight from about 12,000 to 18,000, is employed as the plastic material message carrier. Accurate pit reflection and minimum birefringence in the compact disc requires the use of a plastic material which has great flowability, or in other words, a very low melt viscosity. Dimensional stability and ductility are also important product attributes. Also desirable is excellent processability of the material as manifested by minimum cycle time.
Various polycarbonates have been utilized in the compact disc area. A recently issued U.S. Pat. No. 4,734,488, discloses a polycarbonate which must have an aryl or aralkyl group attached to the carbon atom separating the two phenols and a low molecular weight. The aforementioned U.S. Pat. No. 4,514,357 provides further examples of such materials, specifically bisphenol-A polycarbonate. The example of the end group used in the aforementioned '357 patent is a paratertiary butyl phenol.
It has now been found that paracumylphenol endcapped polycarbonate with a certain melt viscosity range as measured by Kasha Index, provides significant advantages over the prior used compact disc materials. Advantages include improved ductility as measured by 1/8 inch Notched Izod impact and decreased cycle time.